Welcome to the world of sulfuric acid
I remember a single time where it hasn't worked. I was working at a summer camp in Maine and a septic tank pump had jammed. It was the showers' tank, so I thought, "no biggie, I'll just give it a normal shot of drain opener". It was entirely made of cast iron, anyway. After a good flushing of the said substance, the motor was still only buzzing without movement, so I had to service it entirely. When I opened it, I discovered a plug of hair that had been curiously attacked by the acid. It was so dense that after a 15 minute exposition the dangerous substance, it had its top half bleached blonde, and the bottom half still black
EDIT: my bad, The Works use hydrogen chloride, not sulfuric acid. That means it doesn't smell that bad.